The present invention relates to a synchronous motor comprising a stator for generating a rotary magnetic field, for rotating and driving by making use of a reluctance torque.
In a conventional general synchronous motor, a stator is formed by integrally projecting plural teeth from a ring-shaped yoke to its inner circumferential side. This stator is fabricated by laminating stator plates having plural teeth projecting to the inner circumferential side. It also comprises a stator core forming slots among these teeth, and windings are wound in these slots by distributed winding. The distributed winding is a winding method for winding distant teeth through slots. The rotor is composed by burying plural permanent magnets for magnetic poles in the outer circumference of the rotor core, and mounting a rotary shaft in the center. magnets for magnetic poles in the outer circumference of the rotor core, and mounting a rotary shaft in the center.
In this way, by burying permanent magnets inside the rotor, the buried permanent magnet motor can utilize not only the magnet torque but also the reluctance torque, in which the reluctance torque is generated in addition to the magnet torque by the permanent magnets, as an inductance difference occurs between the inductance Ld in the direction of the d-axis which is a direction for coupling the center of the permanent magnet and the rotor center, and the inductance Lq in the direction of the q-axis which is a direction rotated 90 degrees of electrical angle from the d-axis. This relation is shown in formula (1).
T=Pn{"psgr"a X Iq+xc2xd(Ldxe2x88x92Lq)xc3x97Idxc3x97Iq}xe2x80x83xe2x80x83(1)
where
Pn: number of pole pairs
"psgr" a: interlinkage magnetic flux
Ld: d-axis inductance
Lq: q-axis inductance
Iq: q-axis current
Id: d-axis current
Formula (1) shows a voltage equation of dp conversion. For example, in a surface magnet motor, since the permeability of the permanent magnet is nearly equal to that of air, both inductance Ld and Lq in formula (1) are nearly equal values, and the reluctance torque portion expressed in the second term enclosed in braces in formula (1) does not occur. enough to increase the difference of (Ldxe2x88x92Lq). The inductance L, which expresses the degree of ease of passing of magnetic flux, is proportional to N,Q (number of turns of teeth), and hence by increasing the number of turns on the teeth, the difference of (Ldxe2x88x92Lq) becomes larger, so that the reluctance torque can be increased. However, if the number of turns is increased in order to utilize the reluctance torque more, as the number of turns increases, the winding group projecting to the stator end surface, that is, the coil end becomes larger. Hence, to rotate and drive the motor efficiently, if attempted to make use of the reluctance torque, the coil end becomes larger, and the motor itself is increased in size.
In the distributed winding, moreover, by turning windings plural times, a winding ring is formed, and this winding ring is inserted into the teeth, and the periphery of the winding ring becomes longer than the periphery of teeth. Still more, in the distributed winding, since the teeth are wound through slots, the windings cross each other. Thus, in the distributed winding, the winding projects from the stator end, and the windings cross each other to increase the size of the coil end.
Hence, if attempted to drive the motor efficiently by making use of the reluctance torque, the motor size becomes larger. To the contrary, if the motor is reduced in size, the output of the motor drops.
In the air-conditioner, refrigerator, electric vehicle, etc., however, a motor of large output and small size is required.
Incidentally, the magnetic pole portion at the end of the teeth in the stator is formed wider in the peripheral direction.
Between the adjacent magnetic pole portions, however, since openings are formed for laying down windings in the slots, the interval of ends of teeth must be formed wider in the peripheral direction. That is, because of the distributed winding, an opening for inserting the winding ring in the teeth is needed.
Incidentally, the gap between the stator inner circumference and the rotor outer circumference is generally set uniform on the whole periphery except for the openings of the slots.
In such conventional constitution, at the stator side, since there is an opening for a slot between magnetic pole portions, an insulating portion in the peripheral direction is formed in the distribution of the magnetic flux leaving the magnetic pole portions, which produced a problem of occurrence of cogging torque during rotor rotation. At the rotor side, when the distribution of the magnetic flux leaving its outer circumference is brought closer to sine waveform, the cogging torque can be decreased, but since the gap between the stator inner circumference and rotor outer circumference is uniform, the magnetic resistance in this gap is constant on the whole periphery, and in the joining portions of the ends of the permanent magnets, the magnetic flux distribution changes suddenly, and the cogging torque increases. Thus, the cogging torque increasing factors are combined at the stator side and rotor side, and a large cogging torque is caused.
The motor of the invention comprises a stator core having plural teeth and slots provided among these teeth, a winding making a single turn around the teeth, and a rotor incorporating plural permanent magnets, being constituted to rotate and drive by making use of reluctance torque, in which the winding does not cross because of a single turn, and the coil end can be decreased in size.
Moreover, in the core composed by combining plural independent core elements in an annular form, since the winding is turned in the portion of a slot recess formed at both sides of the teeth of the core element, and the winding is wound about the core element, the winding can be applied on the stator in compact arrangement. Moreover, since the winding is not turned in the adjacent state of teeth, it is not necessary to keep a wide opening between the ends of teeth, so that the interval of ends of teeth can be narrowed.
Further, in the stator core composed by coupling ends of plural core elements, and folding the core element group with bent ends into an annular form, since the winding is turned in the slot shape recess portion formed at both sides of the teeth of the core elements, when winding around the teeth, the end interval of teeth can be widened, and the winding can be applied around the teeth in compact arrangement. Moreover, since the ends are coupled, position setting when assembling is easy.
Further, the clearance between the confronting surface of teeth of the permanent magnet and the outer circumference of the rotor core is wider in the central part than in the end portion of the permanent magnet, and the reluctance torque can be utilized effectively.
Further, since the shape of the permanent magnet is projecting toward the center of the rotor in its middle, the reluctance torque can be utilized effectively.
Further, since the width between the adjacent permanent magnets is 0.15 to 0.20 of the width of teeth confronting two magnetic poles (two permanent magnets), the torque ripple of the motor can be suppressed.
Further, the leading end of the magnetic pole portion of the inner circumferential side of the teeth is projecting in the peripheral direction across a slight gap between the ends of the teeth, and the gap between the teeth and rotor outer circumference is nearly constant, so that useless magnetic flux does not flow at the ends of the teeth.
Further, as the leading end of the magnetic pole portion of the inner circumferential side of the teeth is projecting in the peripheral direction so as to connect between ends of the teeth, the gap between the teeth and rotor outer circumference may be continuous.
Further, by setting the width b of the opposite sides of the ends of teeth at b less than 0.6 mm, the magnetic flux is saturated at the ends of the teeth.
Further, the incorporated permanent magnets are thinner in the permanent magnet positioned ahead in the rotor rotating direction than therefor the permanent magnet rear portion, so that the quantity of the permanent magnets may be decreased without lowering the torque.
Further, the profile of the adjacent portions of the permanent magnets is a recess form corresponding to the disk-shape profile positioned outside of the center of the permanent magnet, and the magnetic resistance is increased in the adjacent portions of the permanent magnets, so that the magnetic flux distribution may be close to a sine waveform.
Further, the length of the rotor outer recess positioned outside of the adjacent portions of the permanent magnets should be properly corresponding to the angle of 0.2 to 0.4 of the central angle of the one pole portion of the rotor core.
Further, the gap between the rotor outer recess and teeth should be properly two or more times of the gap between the rotor outer circumference and the teeth.
Further, when the incorporated permanent magnets have two layers, the q-axis inductance increases, and the reluctance torque portion is maximized.
Further, the interval is properly a value set larger than ⅓ of the width of the teeth.
Further, when the winding is a flat square wire, the occupation rate can be enhanced more than in the case of round wire. In particular, the winding of flat square wire is suited to concentric concentrated winding around the teeth.